There is a continuing need for coatings that protect surfaces against adverse environments. Protective coatings are particularly needed for transportation vehicles, especially aircraft. Aircraft surfaces are subjected to erosion from wind and airborne particulate, water, fuel, and sunlight/UV exposure. Protective surface coatings must be flexible and adherent at temperature extremes, particularly low temperatures. It is also desirable that aircraft protective coatings be decorative, especially for commercial aircraft where logos and color schemes are used for carrier differentiation. Therefore, such coatings must be easily and permanently pigmented.
Marine environments present unique challenges to protective coatings for boats and ships of all sizes. In particular, ocean-going craft are subject to extremes of weather and water temperature, an environment that is corrosive to most metals, and organisms, such as molds, slimes and barnacles whose presence on ship's hulls is detrimental. A film-based coating that can discourage organism growth and provide weatherability has not been described heretofore.
Typically, clear or pigmented liquid coatings are used as protective coatings, but these suffer from a number of drawbacks, most notably the use of volatile organic compounds (VOCs) as solvents for their preparation and application. An increasing number of restrictions on VOCs has led to development of water-borne and high-solids coatings, the use of which has limitations due to long drying times, slow cure rates, and inadequate weatherability. Adhesively-applied pigmented films have been proposed as alternative protective coatings. However, films that are, e.g., cost-effective, easily conformed to irregular surfaces and are unaffected by harsh environments have not been found.
Films and coatings comprising fluoro-containing polymers (i.e., polymers prepared from monomers that are fluorinated, preferably highly fluorinated, most preferably perfluorinated) are known and their inertness toward moisture, many solvents, and weathering conditions is known. For example, TEFLON.TM. is a poly(tetrafluoroethylene) compound that has found considerable use as a repellant for rain when incorporated into or spray-applied to clothing, upholstery, and other fabrics. However, fluoro-containing polymers are generally non-polar and do not easily adhere to many common surfaces such as wood, metals, and other polymers. In addition, fluoro-containing polymers generally are more expensive than their hydrocarbon polymer counterparts. Improved, cost-effective, strongly-adhering, long-lasting fluoro-containing polymer protective coatings are continually in demand.
Interpenetrating polymer networks (IPNs), systems comprising two independent crosslinked polymer networks, have been described. See, for example, Encyclopedia of Polymer Science and Engineering Vol. 8; John Wiley & Sons, New York (1984) p. 279 and L. H. Sperling, "Interpenetrating Polymer Networks and Related Materials," Plenum Press, New York (1981). In particular, IPNs comprising acrylate and urethane networks have been prepared by either sequential or simultaneous (but independent) polymerization of free-radically polymerizable ethylenically-unsaturated acrylate-type monomers and urethane precursors (i.e., polyisocyanate and polyhydroxy coreactants). See, for example, U.S. Pat. Nos. 4,128,600, 4,342,793, 4,921,759, 4,950,696, 4,985,340, 5,147,900, 5,256,170, 5,326,621, 5,360,462, and 5,376,428.
Free-standing protective and/or decorative multi-layer films for outdoor use (e.g., outdoor signs, automobile bodies) are known. Typically, such films comprise an adhesive layer, a film layer that may optionally be pigmented, and an overlay or protective layer. Effective protective films must adhere strongly to the substrate (which is often a metal or an already-coated metal) and withstand challenges from heat, oxidants, solvents, sunlight, scratches, and impinged objects such as hailstones and rocks while maintaining their gloss or other decorative aspects, and, in many cases, be easily removable without leaving residual adhesive. See, for example, U.S. Pat. Nos. 5,387,304, 5,306,548 and 5,334,450, 5,378,520 and 4,808,471; European Patent Application Nos. 359,532 and 519,278 and PCT patent application Nos. 92/22619 and 94/099983.
U.S. Pat. No. 5,009,936 describes a transparent top coat applied to a conventional finish coat using a wet-on-wet process. A transparent acrylic layer, comprising functionalized acrylic oligomers and a melamine-type crosslinker is coated, while wet, with a transparent fluorine-containing polymer layer comprising a fluoro-containing polymer that may have hydroxyalkyl or carboxyalkyl functionality and a crosslinker that may comprise a polyisocyanate. The two layers are thermally cured simultaneously. IPN carrier films are not disclosed.
U.S. Pat. No. 4,921,759 describes a transparent plastic sheet prepared by first forming a thin layer of acrylic monomer(s) and free-radical initiator or hydroxy-functional acrylic polymer(s) on a support, covering the acrylic(s) with a reactive mixture of polyisocyanate(s) and polyol(s), then heating the construction. When the construction is cured, the acrylic layer is said to interpenetrate the urethane layer such that no distinct surface layer is observed. Fluoroacrylate layers are not described.
U.S. Pat. No. 4,844,955 describes a multilayer article comprising a thin, thermoplastic cosmetic layer chemically bonded to a cross-linked, isocyanate-modified, thermosetting unsaturated substrate resin. The thermoplastic layer can itself be multilayered, and can comprise, e.g., an acrylic resin or a polyvinylidene fluoride resin or a resin having chemical functionality. The substrate can be a polyester resin or a polyether resin, and can also contain acrylate monomers. On heating together, reactive groups of each layer combine chemically to form a strong interlayer bond. Provision is also made for use of a tie layer that contains chemical groups reactive towards both layers. IPN substrates are not described, nor are fluoroacrylate cosmetic layers.
A number of methods are known for affecting the appearance and performance of film materials, among which is the imposition of a regular or irregular pattern on a surface of the film. The pattern may impart desirable characteristics to the film, such as gloss, reflection-, anti-reflection-, or partial reflection of light, anti-blocking, or improved physical strength. Patterns can be formed by embossing, molding, etching, engraving, or any number of similarly effective means. See, for example, U.S. Pat. No. 4,986,496, particularly Examples 4 and 5.